AC-to-DC charge pump having a charge pump and complimentary charge pump

ABSTRACT

An improved AC-to-DC charge pump for use, for example, in voltage generation circuits. In one embodiment, two 2-diode charge pumps are coupled in back-to-back configuration, and adapted to develop a substantially stable voltage on a mid-level rail. In one other embodiment, two 3-diode charge pumps are coupled in back-to-back configuration, and adapted also to develop a substantially stable voltage on a mid-level rail. In one preferred embodiment, all diodes are implemented as current-source-biased MOSFETs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/583,245 filed 5 Jan. 2012 (“Parent Provisional”), and herebyclaims benefit of the filing dates thereof pursuant to 37 CFR§1.78(a)(4). The subject matter of the Parent Provisional, in itsentirety, is expressly incorporated herein by reference.

The subject matter of this application is related to application Ser.No. 13/209,420, filed on 14 Aug. 2011 (“Related Co-application”).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to voltage generation circuitsused in integrated circuits, and, in particular, to charge pump voltagegeneration circuits.

2. Description of the Related Art

In general, in the descriptions that follow, I will italicize the firstoccurrence of each special term of art that should be familiar to thoseskilled in the art of integrated circuits (“ICs”) and systems. Inaddition, when I first introduce a term that I believe to be new or thatI will use in a context that I believe to be new, I will bold the termand provide the definition that I intend to apply to that term. Inaddition, throughout this description, I will sometimes use the termsassert and negate when referring to the rendering of a signal, signalflag, status bit, or similar apparatus into its logically true orlogically false state, respectively, and the term toggle to indicate thelogical inversion of a signal from one logical state to the other.Alternatively, I may refer to the mutually exclusive boolean states aslogic_0 and logic_1. Of course, as is well known, consistent systemoperation can be obtained by reversing the logic sense of all suchsignals, such that signals described herein as logically true becomelogically false and vice versa. Furthermore, it is of no relevance insuch systems which specific voltage levels are selected to representeach of the logic states.

In general, a charge pump performs power conversion. In particular, anAC-to-DC charge pump draws power from an alternating current (“AC”)source to develop one or more direct current (“DC”) power supplies forload circuitry. Typically, the regulation for these power supplies isnot within the charge pump proper. Rather, regulation is often providedby a regulator which will spill excess current so as to maintain asteady DC supply voltage.

Shown in FIG. 1 is a typical integrated system 10 comprising antenna 12,tank circuit 14, AC-to-DC charge pump 16, DC regulator 18, and anexemplary load circuit 20. As is known, to be most efficient, theresonant frequency of the tank circuit 14 must be tuned to the carrierfrequency of a received radio frequency (“RF”) signal. One effectivetechnique for dynamically tuning the resonant frequency is disclosed inthe Related Co-Application.

During operation, as the charge pump 16 draws more current from the tankcircuit 14, the Q will drop, and the available antenna voltage willdecrease. Ultimately, the current which can be supplied by the chargepump 16 is limited by the RF power received by the antenna 12.

The primary requirement of charge pump 16 is to achieve the targetedsupply voltage from the smallest possible antenna signal (high gain) atthe highest possible efficiency. High gain is not required simplybecause the antenna signal is small. Unloaded, the very high Q of thetank circuit 14 can easily achieve voltages in excess of several volts.As the charge pump 16 is energized, the load 20 will pull current fromthe antenna 12 through the charge pump 16. The effective input impedanceof the charge pump 16 will decrease, causing the Q of the system 10 todrop until the input voltage stabilizes at the input voltage that willjust support the current drawn by the regulator 18 and the load 20. Thehigher the gain of the charge pump 16, the smaller the input signalrequired to sustain the circuit load.

Shown in FIG. 2 is a prior art 2-diode (i.e., second-order) charge pump16 a, comprising capacitors 22 and 24, and diodes 26 and 28. Theidealized output voltage of charge pump 16 a is:V _(o)=2*(V _(p) −V _(d))  [Eq. 1]where V_(p) is the (peak-differential) input voltage and V_(d) is theforward diode drop of diodes 26 and 28. The derivation is left to thereader. A somewhat more accurate expression for the output voltage is:V _(o)=2*(a*V _(p) −V _(d))  [Eq. 2]where a is the AC-coupling gain (hereinafter referred to as “couplingefficiency”) from the V_(INP) input to the node 30 (hereinafter referredto as a “flying node”). For convenience of reference, we shallhereinafter refer to any node having a voltage that is substantiallystatic with respect to V_(SS) as a “fixed bias node”. Since V_(SS) isstatic with respect to itself, V_(SS) is, by this definition, a fixedbias node.

The input capacitor 22 should clearly be chosen to make a very closeto 1. We can see that:

$\begin{matrix}{{V_{p}\min} = {\frac{1}{a}*\left( {\frac{V_{o}}{2} + V_{d}} \right)}} & \left\lbrack {{Eq}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

Even with V_(d)˜0, the 2-diode charge pump 16 a would require an inputof at least

$\left( {\frac{1}{a}*\frac{V_{o}}{2}} \right),$or about 1 V_(p) to sustain a 1.8 V output.

To a good approximation, on each cycle all of the load current (for thatcycle) is drawn through both diodes, and the load current is pulled fromV_(in) twice (once each half cycle) while V_(in) is at its maximum(V_(p)). Therefore, neglecting a, the total power drawn from the inputis:P _(in)=2*V _(p) *I _(load)  [Eq. 4]Also, the total power lost in charge pump 16 a (the power dissipated inthe diodes during forward conduction) is approximately:P _(d)=2*V _(d) *I _(load)  [Eq. 5]Finally, the power delivered to the load is:P _(i) =V _(o) *I _(load)  [Eq. 6]and the power efficiency is:

$\begin{matrix}{{PE} = {\frac{P_{l}}{P_{i\; n}} = {{1 - \frac{P_{d}}{P_{i\; n}}} = {\frac{V_{o}}{\left( {2*V_{p}} \right)} = \frac{V_{o}}{\left( {V_{o} + \left( {2*V_{d}} \right)} \right)}}}}} & \left\lbrack {{Eq}.\mspace{14mu} 7} \right\rbrack\end{matrix}$Clearly, to maximize efficiency you must minimize the forward drops ofdiodes 26 and 28.

Shown in FIG. 3 is a prior art 3-diode (i.e., third-order) charge pump16 b, comprising capacitors 32, 34 and 36 and diodes 38, 40 and 42, witha flying node 44. The analysis of this circuit is a bit more complex,but it can be shown that:

$\begin{matrix}{V_{o} = {3*\left( {V_{p} - V_{d}} \right)}} & \left\lbrack {{Eq}.\mspace{14mu} 8} \right\rbrack \\{{V_{p}\min} = {\left( \frac{V_{o}}{3} \right) + V_{d}}} & \left\lbrack {{Eq}.\mspace{14mu} 9} \right\rbrack \\{{PE} = {\frac{V_{o}}{\left( {3*V_{p}} \right)} = \frac{V_{o}}{\left( {V_{o} + \left( {3*V_{d}} \right)} \right)}}} & \left\lbrack {{Eq}.\mspace{14mu} 10} \right\rbrack\end{matrix}$As can be seen, for higher-order charge pumps, the minimum input voltageis reduced at the cost of decreasing efficiency.

Both the 2-diode and the 3-diode charge pumps suffer from a practicalproblem, which is that with V_(INN) tied to V_(SS), V_(INP) swings V_(p)above and below V_(SS). If V_(SS) is tied to the substrate, V_(INP) willtend to forward bias all substrate diodes on V_(INP) on the down swing,unless the V_(p) required to reach the target output voltage is verysmall indeed.

I submit that what is needed is an improved charge pump that providesimproved power efficiency while overcoming the problems discussed above.

BRIEF SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of my invention, I provide anAC-to-DC charge pump having a first pump comprising a first pair ofdiodes, and a second pump comprising a second pair of diodes, with thefirst and second pumps being coupled back-to-back, i.e., complementary,and adapted to develop a substantially stable voltage on a mid-leveloutput.

In accordance with an alternate embodiment of my invention, I provide anAC-to-DC charge pump having a first pump comprising a first trio ofdiodes, and a second pump comprising a second trio of diodes, with thefirst and second pumps being coupled back-to-back and adapted to developa substantially stable voltage on a mid-level output.

In accordance with another embodiment of my invention, I provide anAC-to-DC charge pump having at least a second-order pump adapted todevelop a first stage voltage and a second stage voltage, the secondstage voltage being greater than the first stage voltage. A series-passregulator is adapted to develop with respect to the first stage voltagea supply as a function of a reference voltage less than the first stagevoltage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

My invention may be more fully understood by a description of certainpreferred embodiments in conjunction with the attached drawings inwhich:

FIG. 1 illustrates, in block diagram form, a typical integrated system;

FIG. 2 illustrates, in schematic diagram form, a prior art 2-diodecharge pump;

FIG. 3 illustrates, in schematic diagram form, a prior art 3-diodecharge pump;

FIG. 4 illustrates, in schematic diagram form, a 4-diode charge pumpconstructed in accordance with one embodiment of my invention;

FIG. 5 illustrates, in schematic diagram form, a 6-diode charge pumpconstructed in accordance with one other embodiment of my invention;

FIG. 6 illustrates, in schematic diagram form, a current-source-biasedP-channel MOSFET diode adapted for use in my invention;

FIG. 7 illustrates, in schematic diagram form, a current-source-biasedN-channel MOSFET diode adapted for use in my invention; and

FIG. 8 illustrates, in schematic diagram form, a full implementation ofmy 4-diode charge pump using current-source-biased MOSFET diodes;

FIG. 9 illustrates, in schematic diagram form, a full implementation ofmy 6-diode charge pump using current-source-biased MOSFET diodes;

FIG. 10 illustrates, in schematic diagram form, a bias network adaptedfor use with my 6-diode charge pump shown in FIG. 9; and

FIG. 11 illustrates, in schematic diagram form, a supplementary DC powersource adapted for use with my 6-diode charge pump shown in FIG. 9.

In the drawings, similar elements will be similarly numbered wheneverpossible. However, this practice is simply for convenience of referenceand to avoid unnecessary proliferation of numbers, and is not intendedto imply or suggest that my invention requires identity in eitherfunction or structure in the several embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 4 is a 4-diode charge pump 16 c constructed in accordancewith my invention. In general, my charge pump 16 c comprises capacitors46, 48, 50 and 52, and diodes 54, 56, 58 and 60, with flying nodes 62and 64. In effect, this configuration consists of a complementary pairof substantially independent 2-diode charge pumps arranged back-to-back,with V_(INN) tied to a middle rail, V_(MID). During operation, V_(MID)will tend to settle to V_(o)/2, and V_(SS) will be pumped below V_(INN).As a result, while V_(INN) will appear stationary with respect toV_(SS), V_(INN) and V_(INP) will share a common-mode voltage which isV_(MID), i.e., approximately V_(o)/2. As a result, the forward biasingof substrate diodes is substantially eliminated. In addition, tuning ofthe tank 14 will be much easier to manage.

Shown in FIG. 5 is a 6-diode charge pump 16 d constructed in accordancewith my invention. In general, my charge pump 16 d comprises capacitors68, 70, 72, 74, 76 and 78, and diodes 80, 82, 84, 86, 88 and 90, withflying nodes 92 and 94, and fixed bias nodes 96 and 98. In effect, thisconfiguration consists of a pair of 3-diode charge pumps arrangedback-to-back, with V_(INN) tied to a middle rail, V_(MID). Duringoperation, V_(MID) will tend to settle to V_(o)/2, and V_(SS) will bepumped below V_(INN). As a result, while V_(INN) will appear stationarywith respect to V_(SS), V_(INN) and V_(INP) will share a common-modevoltage which is V_(MID), i.e., approximately V_(o)/2. As a result, theforward biasing of substrate diodes is substantially eliminated. Inaddition, tuning of the tank 14 will be much easier to manage.

My 4-diode charge pump 16 c and 6-diode charge pump 16 d are madesignificantly more efficient through the use of current-source-biasedMOSFET diodes, which make it possible to reduce the forward “diode”drops to less than 200 mV. The current-source biasing used here is anextension of work by X. Wang et al., “A high efficiency AC-DC chargepump using feedback compensation technique,” Proc. of the IEEE AsianSolid-State Circuits Conf., Nov. 12-14, 2007, Jeju, Korea, pp. 252-255(“Wang”). Consider diode 84—if implemented as a conventional,diode-connected N-channel MOSFET, the forward drop of this diode wouldbe in excess of 0.8 V due to the body effect on the N-channel thresholdvoltage. Using a “Medium” V_(t) (M-V_(t)) device, this drop might comedown to 0.65 V. A better solution is to use a P-channel MOSFET withsource, bulk (i.e., the N-well) and gate connected to V_(o). With thisconnection, forward conduction occurs when the drain rises above thecommon source-bulk-gate connection. Not only is there no body effectenhancement of the threshold voltage, the threshold voltage is actuallysuppressed somewhat by a negative body effect as the drain effectivelybecomes the source and V_(sb) becomes greater than 0. Note that there isno need to do active switching of the N-well between the source/drainterminals as they exchange roles (as suggested by Wang) because theforward “diode” drop of the MOSFET (roughly equal to |V_(t)|) is lessthan the forward bias required to appreciably turn on the body diode.Using a M-V_(t) P-channel device in its own N-well reduces the forwarddrop to around 350 mV.

Now consider the current-source-biased P-channel MOSFET diode 100 ofFIG. 6, comprising P-channel MOSFET transistor 102 (referred tohereinafter as a “diode transistor”), P-channel MOSFET transistor 104(referred to hereinafter as a “bias transistor”) and a capacitor 106coupled between node 108 and the “cathode-end” of the P-channel MOSFETdiode 100 (the symbol I prefer to use to represent such a diode is alsoshown in FIG. 6). In the absence of bias current, the source-to-gatevoltage of bias transistor 104 will collapse to zero due to leakage,leaving the diode transistor 102 with effectively a commonsource-bulk-gate connection, as described above. However, in thepresence of a small positive bias current (i.e., leaving the diode 100),the source-to-gate voltage of the bias transistor 104 will increase,providing a partial bias for the diode transistor 102. There are twopoints to note. First, the partial bias for the diode transistor 102must be small enough to keep reverse leakage currents to a minimum.Reverse leakage currents introduce a power dissipation term in the diode100 when it should ideally have zero current. In addition, any currentwhich leaks backwards through the diode 100 must be replaced on the nextforward cycle, again adding to power loss in the diode 100. Second,capacitor 106 needs to be quite large to stabilize the gate bias. Forexample, considering my charge pump 16 d, as V_(INP) swings and couplesinto node 92 (see, FIG. 5), that swing of 2*V_(p) couples through thegate-to-drain capacitance of the diode transistor 102 into the gate biasnode 108. Unfortunately, this coupling is in exactly the wrongdirection. As node 92 swings down (diode transistor 102 is off), thiscoupling increases the source-to-gate bias increasing the reverseleakage. As node 92 swings up, this coupling reduces the source-to-gatebias, robbing the diode transistor 102 of the desired bias effect.Fortunately, there is little downside to a large capacitor 106 as theparasitic capacitance of this capacitor (preferably implemented as an RFvaractor) will preferably be associated with, i.e., coupled to, a fixedbias node, D_(N), stabilized by a large capacitor. For example, in FIG.5, nodes 96, 98 and V_(O) are all fixed bias nodes, so that diodes 80,84 and 88 may each be replaced with a respective P-channel MOSFET diode100.

Now consider the diode 82 (see, FIG. 5). In this position, the N-well(and all of the parasitic capacitance associated with it) loads flyingnode 92, which swings (a*2*V) from peak to trough and back again duringeach cycle. In this position, the parasitic capacitance directlydegrades the coupling efficiency a, which has a serious detrimentalimpact on the gain and efficiency of the charge pump 16 d. This problemcan be solved by using a current-source-biased N-channel MOSFET diode110, comprising N-channel MOSFET diode transistor 112, N-channel MOSFETbias transistor 114, and capacitor 116 coupled between node 118 and the“anode-end” of the N-channel MOSFET diode 110 (the symbol I prefer touse to represent such a diode is also shown in FIG. 7). As a result ofsubstituting N-channel MOSFETs, the common source-gate node is to the“P-side” (i.e., the “anode-side”) of diode 82. Accordingly, diode 82turns on when the “drain” at node 92 swings below the “source” at node96. The N-channel diode transistor 112 would ordinarily suffer from alarge forward drop due to body effect enhancement of the thresholdvoltage. Fortunately, this body effect is shared by the bias transistor114, so the partial gate-to-source bias will effectively remove theenhanced threshold voltage of the diode transistor 112. Also, byimplementing diode 82 as an N-channel diode 110, the parasiticcapacitance associated with the large bias capacitor 116 appears on node96, which, like V_(o), is a fixed bias node with a large capacitor 70.Furthermore, in FIG. 5, since nodes 98 and V_(SS) are also fixed biasnodes, diodes 86 and 90 may also be replaced with a respective N-channelMOSFET diode 110.

A complete 4-diode charge pump 16 e is shown in FIG. 8 where I have usedmy custom diode symbols (see, FIG. 6 and FIG. 7). The capacitors 46 and50 are preferably implemented as RF varactor capacitors of roughly 1 pF.The bottom-plate parasitic capacitance of these capacitors is coupled tothe input (V_(INP)) to allow maximum coupling into nodes 62 and 64. Thisparasitic capacitance will appear directly as an input capacitance termgiven the much larger decoupling capacitors which provide a return pathfrom V_(SS) to V_(INN). The two large capacitors to V_(INN) (48 and 52)are preferably also implemented as RF varactors to achieve highcapacitance density with low series resistance. The size of these “fast”capacitors at the output nodes (between V_(o) and V_(INN), and V_(INN)and V_(SS)) is critical to achieving the best possible efficiency. Ihave empirically determined that roughly 20 pF each was required tocapture 99% of the potential gain and efficiency. Sizing of the diodetransistors is a trade-off between the lower V_(d) achieved withincreased width versus degradation of the AC coupling into nodes 62 and62 which occurs with larger devices.

A complete 6-diode charge pump 16 f is shown in FIG. 9 where I have usedmy custom diode symbols (see, FIG. 6 and FIG. 7). The “flying”capacitors 68 and 74 are preferably implemented as RF varactorcapacitors of roughly 1 pF. The bottom-plate parasitic capacitance ofthese capacitors is coupled to the input (bottom-plate (V_(INP)) toallow maximum coupling into nodes 92 and 94. This parasitic capacitancewill appear directly as an input capacitance term given the much largerdecoupling capacitors which provide a return path from V_(SS) toV_(INN). The four large capacitors to V_(INN) (70, 72, 76 and 78) arepreferably also implemented as RF varactors to achieve high capacitancedensity with low series resistance. The size of these “fast” capacitorsat the output nodes (between V_(o) and V_(INN), and V_(INN) and V_(SS))is critical to achieving the best possible efficiency. I haveempirically determined that roughly 20 pF each was required to capture99% of the potential gain and efficiency. Sizing of the diodetransistors is a trade-off between the lower V_(d) achieved withincreased width versus degradation of the AC coupling into nodes 92 and94 which occurs with larger devices. The bias network, shown in FIG. 10,runs from a 25 nA input current through 1:1 mirrors to feed the biastransistors—for convenience of reference, I have labeled the biascurrent supply nodes to indicate an associated one of the diodes in FIG.9, e.g., node I_(B8o) supplies bias current I_(Bias) for diode 80. Theeffective bias of the diode transistors (see, FIG. 9) is controlled byscaling of the finger counts of the bias transistors relative to thediode transistors. With my design, the target voltages and load currentscan be supported from an input voltage of 520 mV_(p) (368 mV_(rms)) atalmost 58% efficiency at room temperature and typical semiconductormanufacturing process.

As will be recognized by those skilled in this art, charge pump 16 f isa sixth-order pump, developing with respect to node V_(SS) a first stagevoltage on node 98, a second stage voltage on node 96, and a third stagevoltage on the output node V_(o). It will also be realized that thesecond stage voltage is higher than the first stage voltage, and thatthe third stage voltage is higher than the second stage voltage. If, ina particular application, an intermediate voltage is desired less thanV_(o), then, rather than regulating down from Vo, it will be more powerefficient to develop such voltage from either the second stage voltagenode 96, i.e., V_(MID), or the first stage voltage node 98, asappropriate.

Shown in FIG. 11 is a series-pass regulator 124 adapted in accordancewith one embodiment of my invention to develop a supplemental DC supplyfrom the second stage voltage node 96 of the 6-diode charge pump 16 fillustrated in FIG. 9. I couple between V_(o) and V_(SS) a smallconstant-current source 126 in series with a resistor 128 to develop thedesired voltage, V_(REF), on one input of an operational amplifier(“op-amp”) 130. Applying the output of the op-amp 130 to the gate of anN-channel MOSFET transistor 132 sources the desired supplementary powerat node V_(DD′). By feeding back V_(DD′) to the other input of op-amp130, the gate voltage of transistor 132 will be adjusted until V_(DD′)is substantially equal to the desired V_(REF). Continuing the aboveexample, assume that the desired V_(REF) is 1.0V, then thisconfiguration requires a drop from only 1.2V (the second stage voltage)rather than from 1.8V (the third stage voltage), thereby realizingsubstantial improvement in overall pump efficiency. Of course,transistor 132 could also be coupled to the second stage voltage node96, V_(MID) (e.g., 0.9V) or to the first stage voltage node 98 (e.g.,0.6V).

In the description set forth above, I have chosen to disclose myinvention in the context of paired back-to-back independent chargepumps, each at least second-order. However, it will be clear to thoseskilled in this art that my invention can be used effectively inconfigurations comprising only a single charge pump of second-order orhigher. When implementing my invention in such configurations, eachdiode that has its cathode-end associated with a fixed bias node shouldbe implemented as a P-channel MOSFET diode, and each diode that has itsanode-end associated with a fixed bias node should be implemented as anN-channel MOSFET diode. By way of example, in the prior art second-ordercharge pump shown in FIG. 2, the fixed bias nodes are V_(O) and V_(SS);and; thus, in accordance with my invention, diode 26 should beimplemented as an N-channel MOSFET diode, and diode 28 should beimplemented as a P-channel MOSFET diode. In general, therefore, myinvention can be applied to any charge pump of second-order or higher,provided that the design incorporates at least one fixed bias node,which will normally be the case.

Thus it is apparent that I have provided an improved AC-to-DC chargepump that provides improved power efficiency while overcoming theproblems inherent in prior art charge pumps. Therefore, I intend that myinvention encompass all such variations and modifications as fall withinthe scope of the appended claims.

What we claim is:
 1. An AC-to-DC charge pump comprising: a charge pumpoperable to convert an AC (alternating current) input voltage into a DC(direct current) voltage, wherein the charge pump includes: a flyingnode capacitor; a fixed node capacitor; a first diode circuit; a seconddiode circuit; a third diode circuit; and an output capacitor, wherein afirst node of the flying node capacitor is coupled to a positive leg ofthe AC input voltage (V_(INP)) and a second node of the flying nodecapacitor is coupled to a flying node, wherein an anode of the firstdiode circuit is coupled to the V_(INP) and a cathode of the first diodecircuit is coupled to a bias node, wherein an anode of the second diodecircuit is coupled to the bias node and a cathode of the second diodecircuit is coupled to the flying node, wherein an anode of the thirddiode circuit is coupled to the flying node and a cathode of the thirddiode circuit is coupled to an output node, and wherein a first node ofthe output capacitor is coupled to the output node and a second node ofthe output capacitor is coupled to the middle rail; and a complimentarycharge pump operable to convert the AC voltage into a complimentary DCvoltage, wherein magnitude of the DC voltage is substantially equal tomagnitude of the complimentary DC voltage and wherein the charge pump iscoupled to the complimentary charge pump to add the DC voltage and thecomplimentary DC voltages to produce an output voltage, which has amiddle rail that is coupled to a negative leg (V_(INN)) of the AC inputvoltage.
 2. The charge pump of claim 1 further comprises: each of thefirst and third diode circuits includes a current-source-biasedP-channel MOSFET diode; and the second diode circuit includes acurrent-source-biased N-channel MOSFET diode.
 3. The charge pump ofclaim 1 wherein the complimentarily charge pump comprises: a flying nodecapacitor; a fixed node capacitor; a first diode circuit; a second diodecircuit; a third diode circuit; and an output capacitor, wherein a firstnode of the flying node capacitor is coupled to a positive leg of the ACinput voltage (V_(INP)) and a second node of the flying node capacitoris coupled to a flying node, wherein a cathode of the first diodecircuit is coupled to the V_(INP) and an anode of the first diodecircuit is coupled to a bias node, wherein a cathode of the second diodecircuit is coupled to the bias node and an anode of the second diodecircuit is coupled to the flying node, wherein a cathode of the thirddiode circuit is coupled to the flying node and an anode of the thirddiode circuit is coupled to an output node, and wherein a first node ofthe output capacitor is coupled to the output node and a second node ofthe output capacitor is coupled to the middle rail.
 4. The charge pumpof claim 3 further comprises: each of the first and third diode circuitsincludes a current-source-biased N-channel MOSFET diode; and the seconddiode circuit includes a current-source-biased P-channel MOSFET diode.5. An integrated system comprising: an antenna; a tank circuit coupledto the antenna; an AC-to-DC charge pump circuit coupled to the tankcircuit, wherein the charge pump circuit includes: a charge pumpoperable to convert an AC (alternating current) input voltage receivedvia the antenna into a DC (direct current) voltage, wherein the chargepump circuit comprises: a flying node capacitor; a fixed node capacitor;a first diode circuit; a second diode circuit; a third diode circuit;and an output capacitor, wherein a first node of the flying nodecapacitor is coupled to a positive leg of the AC input voltage (V_(INP))and a second node of the flying node capacitor is coupled to a flyingnode, wherein an anode of the first diode circuit is coupled to theV_(INP) and a cathode of the first diode circuit is coupled to a biasnode, wherein an anode of the second diode circuit is coupled to thebias node and a cathode of the second diode circuit is coupled to theflying node, wherein an anode of the third diode circuit is coupled tothe flying node and a cathode of the third diode circuit is coupled toan output node, and wherein a first node of the output capacitor iscoupled to the output node and a second node of the output capacitor iscoupled to the middle rail; and a complimentary charge pump operable toconvert the AC voltage into a complimentary DC voltage, whereinmagnitude of the DC voltage is substantially equal to magnitude of thecomplimentary DC voltage and wherein the charge pump is coupled to thecomplimentary charge pump to add the DC voltage and the complimentary DCvoltages to produce an output voltage, which has a middle rail that iscoupled to a negative leg (V_(INN)) of the AC input voltage.
 6. Theintegrated system of claim 5 further comprises: each of the first andthird diode circuits includes a current-source-biased P-channel MOSFETdiode; and the second diode circuit includes a current-source-biasedN-channel MOSFET diode.
 7. The integrated system of claim 5, wherein thecomplimentary charge pump comprises: a flying node capacitor; a fixednode capacitor; a first diode circuit; a second diode circuit; a thirddiode circuit; and an output capacitor, wherein a first node of theflying node capacitor is coupled to a positive leg of the AC inputvoltage (V_(INP)) and a second node of the flying node capacitor iscoupled to a flying node, wherein a cathode of the first diode circuitis coupled to the V_(INP) and an anode of the first diode circuit iscoupled to a bias node, wherein a cathode of the second diode circuit iscoupled to the bias node and an anode of the second diode circuit iscoupled to the flying node, wherein a cathode of the third diode circuitis coupled to the flying node and an anode of the third diode circuit iscoupled to an output node, and wherein a first node of the outputcapacitor is coupled to the output node and a second node of the outputcapacitor is coupled to the middle rail.
 8. The integrated system ofclaim 7 further comprises: each of the first and third diode circuitsincludes a current-source-biased N-channel MOSFET diode; and the seconddiode circuit includes a current-source-biased P-channel MOSFET diode.